Stress often affects food preference and intake. Although stress can cause hypophagia, abundant studies consistently reveal that mild to moderate acute stress increases sweet high-fat food preference and intake stress-induced emotional eating may be attributed to diminished serotonergic (5-HTergic) neurotransmission or function.
Serotonine levels in the brain have been linked with mood, alertness, vigilance, sleep onset and quality, anxiolytic effects, depression, affective reaction control, appetite and sexual behavior. Many publications exist in which changes in brain serotonin levels are correlated with the availability of the natural amino acid L-tryptophan (Trp or W). Because of this correlation, methods to increase plasma tryptophan levels have received a lot of attention. Tryptophan quantities of around 1 gram/day per individual have been reported to yield clinically significant effects (Markus et al., Am. J Clin. Nutr 2005;81, 1026-1033). One method to increase plasma tryptophan levels involves the consumption of protein preparations enriched in the whey protein alpha-lactalbumin. Alpha-lactalbumin preparations are readily available and have a relatively high tryptophan concentration. However, approaches in which the alpha-lactalbumine is provided as such, see for example DE 4130284 and JP 2279700, do not take into account that the main determinant of brain tryptophan and serotonin levels is not plasma tryptophan concentration alone, but the socalled Trp/LNAA ratio (Fernstrom and Wurtman. Science 1971, 173, 149-152). This Trp/LNAA ratio represents the molar ratio of tryptophan relative to the levels of Large Neutral Amino Acids (LNAA:, i.e. the sum of tyrosine, phenylalanine, leucine, isoleucine and valine) in plasma. These LNAA compete with tryptophan for uptake into the brain, presumably because the same transport mechanism across the blood-brain barrier is used. Therefore, the most effective way of increasing brain tryptophan concentrations is to supply preparations with a high Trp/LNAA ratio. A number of publications a.o. WO 02/46210, refer to the preparation of peptide fractions from alpha-lactalbumin having improved Trp/LNAA ratio's.
Obviously the use of free tryptophan, i.e. the free amino acid, would provide the simplest and cheapest approach to provide preparations with a high Trp/LNAA ratio. However, in many countries legislation exists that tightly regulates the supply of free tryptophan. The maximal allowable free tryptophan levels in its various application forms vary per country. To supply additional dietary tryptophan in a more natural way, more recent approaches aim at providing tryptophan rich proteins. As mentioned, alpha-lactalbumin as well as its hydrolysates have gained popularity as a safe option to enhance plasma tryptophan levels.
WO2008/052995 and WO02/46210 disclose a process to produce a composition comprising a tryptophan-containing peptide and having a Trp/LNAA ratio of more than 0.15 which comprises hydrolyzing lysozyme, preferably hen eggs lysozyme, to prepare a hydrolysate having a DH of between 5 and 45.